This invention relates in general to a method of treating silicon and in particular, to such a method that results in the fabrication of an MNOS field effect transistor with improved memory retention characteristics.
Heretofore, in the manufacture of the MNOS transistor device structure, the critical SiO.sub.2 layer has been formed by employing vapor or liquid chemical techniques. The SiO.sub.2 layer is only about 25 to 50 angstroms in thickness but its composition is significant in determining transistor turn-on threshold voltage and Si.sub.3 N.sub.4 /SiO.sub.2 retention characteristics. With the vapor and liquid techniques, it has been difficult to precisely control the oxidation reaction in which SiO.sub.2 is produced in the surface of the silicon wafer. This is because one cannot precisely control the quantity of oxygen atoms that are available for oxidation of the silicon. In addition, in the liquid and vapor chemical techniques, it is difficult to control the uniformity of the oxidation reaction across the silicon wafer and also to control the amount of oxygen atoms introduced into the silicon from one oxidation run to another.
Moreover, in the liquid and vapor chemical techniques, foreign atoms are introduced into the silicon during the oxidation. These foreign atoms or contaminants remain in the silicon oxide and contribute to the degradation of subsequent device structures.